Building Antweights with Servo motors

A lot of folks avoid using servo motors for building antweight fighting robots. The main complaint is that servo powered machines tend to be pretty slow. Well for the most part this is true. But servos do have a lot of power to offer. Most standard servos are designed to run at 4.8 to 6 VDC. At this voltage range they do tend to be pretty slow. But thanks to the magic of over volting you can definitely wake them up.

I've run standard Futaba S3001, S3003 and S3004 (hacked for full rotation) at 4.8 VDC, 6 VDC, 9 VDC, 12 VDC, 14 VDC, 16 VDC.

People keep asking me how do you do this without frying the servo or radio electronics?

Well kids the secrete is....

I remove all of the servo electronics and just run wires directly to the servo motors.

Basically I use them as mini gear motors.

When I first built an antweight, like most folks that build much larger robots, I had no parts for an Ant. So I built a simple 4.8 VDC receiver powered 2 servo motor driven plastic base plate with wheels.

Not to exciting but it was easy to build and I noticed that standard 43 oz in servos even at 4.8 VDC are pretty torquey.

Hmm I wondered, What happens if you kick up the voltage a bit. Well this crazy Idea became the basis for the first version of a robot called SnackBreak.

SnackBreak Ver 1.0
SnackBreak was built using several parts borrowed from The Robot Club.

It used a Futaba receiver and 2 Team Delta RCE 220 duel ended switches wired to work as h-bridges.



Having built much larger robots I'm very familiar with the reliability of  Team Delta electronics. Of course these switches are way over kill for powering a servo. But they provided an easy and familiar solution. I decided to run the servo motors at 9 VDC using a Radio Shack rechargeable Nicad battery.

Of course running the robot with a 9 VDC battery left me with a small problem.
The receiver and the control side of the Team Delta Boards run at 5 VDC.

So I went back to Radio shack and bought a 7805 5 VDC voltage regulator. Cool now everything will run off of the single 9 VDC source with a bit of wiring. See drawing.


 

Team Delta boards wired as H bridges powering servo motors directly at 9 VDC to whatever you want to risk (well the 7805 regulator is rated up to 35 VDC input ) but it is much happier at up to about 15 VDC. Also the 7805 regulator must be mounted to a heat sink or it will over heat. I bolted it to the aluminum frame of the robot.

Tech note: 7805 regulators are designed to put out a maximum of 1 amp at 5 VDC with a heat sink. That's fine for powering a receiver but but don't try running servos or motors with it. It will go into thermal shutdown or burn up.

Any ways after I had all of this stuff crammed into SnackBreak.. I tested the robot and was much more satisfied with the speed and power increase. One problem in using the two Team Delta boards in an Ant is they weigh 1.4 oz's EACH.


This is the first version of Snack Break Unfortunately I don't have a picture of all of the electronics and wiring crammed inside. This version has the tires borrowed from an RC car.

I've bought many cheapo RC cars just for the tires. The folks at Radio Shack thought I was crazy for buying complete RC cars just to use the tires or hack whatever parts I found useful.

Most of the cars we totally stripped within 10 minutes of purchase.

Good safety tip: Never park your RC car next to a Robot Club. ;)

 Not long after this modification I went to Las Vegas and fought SnackBreak at Robo Joust 4 and even won a couple of matches. During this event I got a chance to check out some of the new Sozbot controllers. I was amazed at how small and light that they were compared to what I was using.



 


SnackBreak Ver 2.0

Over volting Servos with the Sozbot duel motor speed controller.


 

This is a Sozbot dual motor controller it is rated at up to 16 VDC and 5 amps of current output. Boy I'll tell ya this little 1.5 inch x 1.5 inch controller works good. For their small size they work just as well as the controllers I use in my Heavyweights and Supers. Oh ya and they only weight 0.42 ozs.

Well as soon as I got back from Vegas I ordered one. I then did the next level modification to Snack Break I removed all of the electronics I was using.

This plus the battery removed over 4 ozs of weight from the robot. Loosing this much weight gave me a chance to UP the voltage again. He He....
I installed two 6 VDC 500 mA (N cell) size Nimh packs wired in series for a total of 12 VDC. I connected the Sozbot controller to the 12 VDC source and the receiver (The controller also has a built in 5 VDC regulator so it powers the receiver through the servo connectors (Very cool)). See drawing...


When I turned on the robot after this Mod I was very impressed with the difference in speed and power. Man 12 VDC really makes servos come alive. The darn little robot would now pull the front end off the ground when I gave it full throttle.

I was really afraid that the servo motors would probably fry under heavy loads so I did a lot of severe testing at 12 VDC. I added 3 lbs of weight to the robot and it barley noticed the difference. I added 5 lbs of weight and then finally 12 lbs of weight sitting on my poor little 1 lb robot and it still kept going with a noticeable scream of the servos gear boxes.


At this point I decided to save it for the next event at the Robot Club.

After Snack Break we built 2 more 12 VDC Sozbot controlled Servo based Ants one was called Furball (Its name started from a nickname I gave it, because of its tendency of leaving chunks of foam rubber all over the arena from its hand made tires)and the other robot was called Wilson.

In March of 2003 Snack Break won the Antweight class using just plain standard servos over volted to 12 VDC with a Sozbot speed controller. It was a very close final against Furball.


Furball with its trademark hand made foam tires (Ant Terrain) Furball went on to become the number one ranked Antweight robot at the Robot Club.
17 wins - 4 losses, 11 kos, 70 points
Driver James J. McLaughlin Jr.

Furball and SnackBreak had so many fights there's no way to count them. We were so evenly powered that usually one of us had to make a driving error for the other to win. See what happens when you teach folks how to build.

The mighty robot Wilson
(Battery's placed directly over the servo motors for maximum traction (Smart))
Tom Bossart built this Ant at the Robot Club it has a lifting arm and we upgraded the drive train from 4.8 VDC to 12 VDC.


Many of the Antweight robots using different motors are faster but in pushing power servos are pretty hard to beat. Snack Break has had a rough life and has fought for hours and hours of continuous combat.

One problem that I finally started having with over volted servos is they really like to strip the plastic gears in the servo gear boxes. It is possible to buy different model servos with metal gears and probably a good idea. I've stripped about 10 sets of plastic gears in the last year or so.

One of the things we also discovered in using servos for drive motors in Ants is, to get much speed out of them you need to use a large diameter tire. I have had good success using Liteflite foam rubber tires in the 3 inch diameter range. I use the LiteFlite's (well because their Lite). The overvolted servos provide plenty of power so a large diameter tire is a great way to increase the robots speed.

Liteflite tires come in many diamters and are available from robot combat.com



Recently SnackBreak fought at the Holiday Games in SanFransisco. It won its first two matches one against a robot that used a rare earth magnet to glue itself to the arena floor. I was told that the magnet produced about 5 lbs of down force to the arena floor. Not bad for a magnet the size of a dime.

SnackBreak pried it loose from the floor twice in that fight and finally pushed it out of the arena.  Then I lost to a nasty spinner when my battle worn battery's finally died for the last time.

Fortunately I purchased some new ones from Jim at RobotCombat.com. I some how didn't notice that the packs I bought had 6 cells instead of 5.

So guess what now the servos are running at 14-16 Volts when fully charged. I'm sure I'm getting really close to the limit of both the servos and the speed control now. And yes it does appear to be a little faster now he he.....


At the Robot club we were always trying new stuff in all of the weight classes. Since we had proven that servos can make a decent drive motor for an Antweight robot we wanted to overvolt servos for use as lifting weapons in the Ants as well.

I found this great artical from the Seattle Robotics Society that shows the servo schematic for many
Futaba servos.

 
 

What the heck lets hack a Futaba servo in a different way. We found that Futaba servos have two chips in their control boards. The BA6688 IC provides the radio signal decoding and reads the positioning resistor (Pot) and the other is the BAL 6686 H-bridge that powers the servos motor. Oh Ooh Steve found another H-bridge to overvolt with. He He.....


This is the pinout of the 6686 H bridge what we did to overvolt the h-bridge was to desolder pin one (VCC) and lift it out of the board, we then attached a wire directly to pin one and connected it to a 12 VDC battery we ran another wire to the receivers ground and connected it to the 12 VDC batterys ground. By isolating pin one we were able to have all of the servos positioning functions and we protected the servo electronics and the receiver from the 12 VDC. And of course we created a servo with a whole lot more speed and lifting power.



Another thing we did was to take the Two servo boards and use them to control a Tamyia duel gear box that we got from the SozBot folks. We used the servo boards that I had already removed and connected their outputs to the gear motors. (One servo board per motor for tank steering)  To save a little weight we  removed the metal pot that the servo uses and borrowed a couple of small 5K pots from a monitor that had been recently destroyed  for center trim adjustment . I considered it Recycling.

We found this to work pretty well and it became a low buck motor control for small gear motors although a true speed controller will work better. It is possible to use the above modifacation to overvolt a set of servos and build a running drive train for a antweight pushybot.
 

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